Planarization process for pre-damascene structure including metal hard mask

ABSTRACT

A planarization process for a pre-damascene structure is described, wherein the pre-damascene structure includes a metal hard mask that is disposed on a first material layer with a damascene opening therein and a second material layer that fills the damascene opening and covers the metal hard mask. A first CMP step is conducted using a first slurry to remove the second material layer outside the damascene opening. A second CMP step is conducted using a second slurry to remove the metal hard mask.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor process. Moreparticularly, the present invention relates to a planarization processfor a pre-damascene structure that includes a metal hard mask.

2. Description of the Related Art

Damascene techniques are frequently used to form interconnectstructures. In a conventional damascene process, a dielectric layer isformed and then patterned using a hard mask to form a damascene openingtherein, a metal layer is formed filling the damascene opening, themetal layer outside the opening is removed through chemical mechanicalpolishing (CMP), and then the hard mask is removed. In the related art,the process of removing the metal layer outside the damascene openingthrough CMP is considered as a planarization process.

However, as the linewidth of semiconductor devices becomes smaller, theconventional SiO or SiN hard mask is no longer satisfactory for therequirements in critical dimension (CD). Therefore, metal hard masks arereported to use in advanced semiconductor processes. In the prior art, ametal hard mask is removed through dry- or wet-etching after the metallayer filling the damascene opening is planarized through CMP.

SUMMARY OF THE INVENTION

Accordingly, this invention provides a planarization process for apre-damascene structure including a metal hard mask, which removes themetal hard mask also through CMP.

In a planarization process of this invention, the pre-damascenestructure includes a metal hard mask that is disposed on a firstmaterial layer with a damascene opening therein and a second materiallayer that fills the damascene opening and covers the metal hard mask. Afirst CMP step is conducted using a first slurry to remove the secondmaterial layer outside the damascene opening, and then a second CMP stepis conducted using a second slurry to remove the metal hard mask.

According to a preferred embodiment of this invention, the firstmaterial layer and the second material layer may include a dielectriclayer and a metal layer, respectively, for forming an interconnectdamascene structure. In such cases, a barrier layer is preferably formedin the damascene opening and on the metal hard mask before the metallayer as the second material layer is formed, while the barrier layer onthe metal hard mask is removed in the second CMP step prior to the metalhard mask.

Moreover, the above damascene opening may be, for example, a dualdamascene opening that includes a trench and a via hole contiguous withthe trench.

According to another embodiment of this invention, the pre-damascenestructure may include a dielectric layer as a first material layer, ametal layer as a second material layer and a barrier layer in thedamascene opening and on the metal hard mask, while the planarizationprocess may include three CMP steps. The first CMP step is conductedusing a first slurry to remove the metal layer outside the damasceneopening. The second CMP step is conducted using a second slurry tosequentially remove the barrier layer on the metal hard mask and themetal hard mask. The third CMP step is then conducted using a thirdslurry to remove a portion of the dielectric layer.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, and are intended toprovide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-3 illustrate a process flow of a planarization process accordingto a first embodiment of this invention.

FIGS. 4 and 5 illustrate different stages in the second CMP step of aplanarization process according to a second embodiment of thisinvention, while FIGS. 1, 2, 4+5 and 3 in sequence illustrate the wholeplanarization process of the second embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

Referring to FIG. 1, a substrate 100 having a prior conductive layer110, a cap layer 120 and a pre-dual damascene structure thereon isprovided, wherein the pre-dual damascene structure will be processedinto a dual damascene structure that electrically connects with theconductive layer 110. The pre-dual damascene structure includes adielectric layer 130 having a trench 150 and a via hole 160 contiguouswith the trench 150 therein, a metal hard mask 140 on the dielectriclayer 130, and a metal layer 180 filling the trench 150 and the via hole160 and covering the metal hard mask 140.

In addition, a barrier layer 170 is preferably formed on the innersurfaces of the trench 150 and the via hole 160 and on the metal hardmask 140 before the metal layer 180 is formed, so as to preventdiffusion of metal atoms from the metal layer 180. The bottom of themetal layer 180 in the via hole 160 is separated from the conductivelayer 110 by the barrier layer 170. The material of the cap layer 120may be silicon nitride (SiN), SiC, SiCN, SiCO or SiCNO, etc., and thedielectric layer 130 may include TEOS-oxide, thermal oxide or low-kmaterial, etc. The material of the metal hard mask 140 may be Ti, Ta, W,TiN, TaN or WN, for example, wherein the metal nitrides are preferable.The barrier layer 170 may include Ta or Ta/TaN, for example, and themetal layer 180 is possibly a copper layer.

Referring to FIG. 2, a first CMP step is conducted using a first slurryto remove the metal layer 180 outside the trench 150, so that aconductive line 180 a and a contact plug 180 b are formed in the trench150 and the via hole 160, respectively. The selectivity of the firstslurry to the metal layer 180 relative to the barrier layer 170preferably ranges from 50:1 to 500:1. When the metal layer 180 includescopper, such a slurry may include SiO2 or Al2O3, H2O2 and water and havea pH value of 1-6. In addition, the first CMP step can be conducted onone platen, or on two separated platens in the same CMP machine toincrease the throughput, as known in the art.

Referring to FIG. 3, a second CMP step is conducted using a secondslurry to sequentially remove the barrier layer 170 on the metal hardmask 140 and the metal hard mask 140. The second CMP step can be furtherconducted to remove a portion of the dielectric layer 130. In such acase, the selectivity of the second slurry to the barrier layer 170relative to the metal layer 180 preferably ranges from 1:1 to 5:1, theselectivity of the second slurry to the barrier layer 170 relative tothe metal hard mask 140 preferably ranges from 1:5 to 5:1, and theselectivity of the second slurry to the barrier layer 170 relative tothe dielectric layer 130 preferably ranges from 0.5:1 to 50:1. When themetal layer 180 includes copper, such a second slurry may include SiO2,H2O2, benzotriazole (BTA) and water as well as have a pH value of 9-13,wherein BTA serves as a copper corrosion inhibitor. The second CMP stepmay also be conducted on one platen, or on two separated platens in thesame CMP machine to increase the throughput, as mentioned above.

Second Embodiment

FIGS. 1, 2, 4+5 and 3 in sequence illustrate the whole planarizationprocess according to the second embodiment of this invention.

In the second embodiment, the substrate 100 having a pre-damascenestructure as shown in FIG. 1 thereon is provided. A first CMP step isconducted to remove the copper layer 180 outside the damascene opening(150+160), as shown in FIG. 2. The slurry and polishing conditionsadopted in the first CMP step can be the same as those mentioned in theabove first embodiment.

Referring to FIGS. 4-5, a second CMP step is conducted using a secondslurry to remove the barrier layer 170 on the metal hard mask 140 (FIG.4) and then remove the metal hard mask 140 (FIG. 5). In the second CMPstep, the selectivity of the second slurry to the barrier layer 170relative to the metal layer 180 preferably ranges from 1:1 to 5:1, theselectivity of the second slurry to the barrier layer 170 relative tothe metal hard mask 140 preferably ranges from 1:5 to 5:1, and theselectivity of the second slurry to the barrier layer 170 or the metalhard mask 140 relative to the dielectric layer 130 ranges from 3:1 to50:1. When the metal layer 180 includes copper, such a second slurry mayinclude SiO2, H2O2, benzotriazole (BTA) and water as well as have a pHvalue of 4-6, wherein the amount of SiO2 is no more than 10 wt % forinhibiting the polishing selectivity to the dielectric layer 130, andBTA serves as a copper corrosion inhibitor. In addition, the second CMPstep may also be conducted on one platen, or on two separated platens inthe same CMP machine to increase the throughput, as mentioned above.

Referring to FIG. 3, a third CMP step is conducted using a third slurryto remove a portion of the dielectric layer 130, so as to ensure that noresidue of the metal hard mask 140 remains to short different conductivelines/contact plugs 180 a/b. When the metal layer includes copper, thethird slurry suitable for TEOS-oxide, thermal oxide or low-k material,etc., may include SiO2, H2O2, benzotriazole (BTA) and water as well ashave a pH value of 9-13. The third CMP step may also be conducted on oneplaten, or on two separated platens in the same CMP machine to increasethe throughput, as mentioned above.

As described above, by applying the planarization process of thisinvention, the metal layer filling the damascene opening as well as themetal hard mask can be removed sequentially through CMP.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of the foregoing, it is intended that the present inventioncovers modifications and variations of this invention provided they fallwithin the scope of the following claims and their equivalents.

1. A planarization process for a pre-damascene structure which includesa metal hard mask that is disposed on a first material layer with adamascene opening therein and a second material layer that fills thedamascene opening and covers the metal hard mask, comprising: conductinga first chemical mechanical polishing (CMP) step using a first slurry toremove the second material layer outside the damascene opening; andconducting a second CMP step using a second slurry to remove the metalhard mask, wherein a composition of the second slurry is different froma composition of the first slurry, wherein the second material layercomprises a metal layer, and the second slurry comprises SiO₂, H₂O₂,benzotriazole (BTA) and water and has a pH value of 9-13.
 2. Theplanarization process of claim 1, wherein the first material layercomprises a dielectric layer.
 3. The planarization process of claim 2,wherein the damascene opening comprises a dual damascene opening.
 4. Theplanarization process of claim 2, wherein the pre-damascene structurefurther comprises a barrier layer in the damascene opening and on themetal hard mask; and the second CMP step removes the barrier layer onthe metal hard mask before removing the metal hard mask.
 5. Theplanarization process of claim 4, wherein selectivity of the firstslurry to the metal layer relative to the barrier layer ranges from 50:1to 500:1.
 6. The planarization process of claim 5, wherein the metallayer comprises copper, and the first slurry comprises SiO₂ or Al₂O₃,H₂O₂ and water and has a pH value of 1-6.
 7. The planarization processof claim 4, wherein the second CMP step further removes a portion of thedielectric layer after removing the metal hard mask.
 8. Theplanarization process of claim 4, wherein selectivity of the secondslurry to the barrier layer relative to the metal layer ranges from 1:1to 5:1; selectivity of the second slurry to the barrier layer relativeto the metal hard mask ranges from 1:5 to 5:1; and selectivity of thesecond slurry to the barrier layer relative to the dielectric layerranges from 0.5:1 to 50:1.
 9. The planarization process of claim 8,wherein the metal layer comprises copper.